1. Field
Embodiments of the present invention relate to an electronic parking brake system to detect malfunction of an electronic parking brake apparatus, and a control method thereof.
2. Description of the Related Art
In general, a brake system is a system which decelerates and stops a vehicle during driving and simultaneously maintains the stopped state of the vehicle. The brake system includes a parking brake apparatus which decelerates and stops a vehicle during driving and simultaneously maintains the stopped state of the vehicle.
The parking brake apparatus is configured such that, when a lever provided at one side of a driver's seat in a vehicle is operated, a parking cable is pulled and then provides braking force to vehicle wheels connected to the parking cable to maintain a stopped state of the vehicle wheels, and, when the lever is released, the parking cable is loosened to release the braking force from the vehicle wheels. Such an operating type of the parking brake apparatus to supply braking force to the vehicle wheels or release the braking force from the vehicle wheels using tension of the parking cable is referred to as a cable puller type.
As to such a cable puller type parking brake apparatus, a driver has to operate the lever whenever the parking brake apparatus is operated, i.e. parking or driving of the vehicle is started, only by driver's intention, and thus use of the parking brake apparatus is very cumbersome. Therefore, an electronic parking brake (EPB) system which enables a parking brake apparatus to be automatically operated by a motor according to an operating state of a vehicle has been developed.
The electronic parking brake (EPB) system operates the parking brake apparatus or stops the operation of the parking brake apparatus and ensures stability in braking in case of emergency in connection with a manual operation mode, a hydraulic electronic control unit (HECU), an engine electronic control unit (ECU), and a traction control unit (TCU) through switch operation.
The above electronic parking brake (EPB) system includes an electronic control unit (ECU), a motor, a gear, a parking cable, and a force sensor, which are integrally formed. Here, the electronic control unit (ECU) receives related data input from the hydraulic electronic control unit (HECU), the engine electronic control unit (ECU), and the traction control unit (TCU) through controller area network (CAN) communication, understands driver's intention, and then drives the motor. Then, the gear is operated by driving the motor, and the parking cable is pulled by the operation of the gear to provide braking force to vehicle wheels, thereby maintaining a stable state of the vehicle. Here, tension of the parking cable is sensed by the force sensor. Further, tension of the parking cable is automatically set based on vehicle conditions and a vehicle gradient, and the set tension of the parking cable and the sensed tension of the parking cable are compared with each other, thereby enabling proper braking force to be applied to the vehicle wheels.
If the force sensor to sense tension of the parking cable malfunctions, sufficient braking force is not supplied, thereby causing serious danger in safety of the vehicle.